1. Field of the Invention
This invention relates to optically-based evaluation of particles suspended in a fluid carrier medium. It is particularly directed to an improved apparatus and method for carrying out interrogation of particles by applying radiation to such particles and detecting a shift in wavelength of radiation emitted by selected ones of those particles.
2. State of the Art
Flow cytometry is a well established technique that is used to determine certain physical and chemical properties of microscopic particles by sensing certain optical properties of the particles. Many books and articles are available detailing aspects of this useful investigational tool. For example, operational principles of, and procedures for use of, modern cytometers are set forth in “Practical Flow Cytometry” by Howard M. Shapiro. Flow cytometry is currently used in a wide variety of applications including hematology, immunology, genetics, food science, pharmacology, microbiology, parasitology and oncology.
In flow cytometry, microscopic particles entrained in a carrier fluid are typically arranged in single-file inside a core stream using hydrodynamic focusing. The particles are then individually interrogated by an optical detection system. The interrogation typically includes directing a light beam from a radiation source, such as a laser, transversely across the focused stream of single-file particles. The light beam is scattered by each particle to produce a scatter profile. The scatter profile may be analyzed by measuring the light intensity at both small and larger scatter angles. Certain physical and/or chemical properties of each particle can then be determined from the scatter profile.
It is also known to apply fluorescing markers to selected particles of interest prior to processing such particles in a cytometer. For example, particles such as blood cells can be “tagged” with fluorescent molecules by using conjugated monoclonal antibodies. The wavelength of the radiation source (typically a laser), is matched to the excitation wavelength of the fluorescing molecule marker. The tagged particles fluoresce in the cytometer when excited by the transversely oriented laser beam. The fluorescence given off by the excited particle can be detected by an appropriately configured detector, which is conventionally mounted transverse to the path of the particles in the interrogation portion of the cytometer. Therefore, cells tagged with fluorescing markers can be easily detected for counting, or other data manipulation.
Unfortunately, flow cytometers are undesirably complex and expensive pieces of equipment. Care must be taken to ensure the machine is set up correctly, and properly calibrated. It would be an advance to provide a robust, inexpensive apparatus that can be used to promote single-file particle travel through an optically based interrogation zone to promote rapid processing of a plurality of different particle-bearing fluid samples.